Mass ocurrence of the larvae of

Dasychira pudibunda in southern Sjślland

By Jens Meulengracht-Madsen & P. Stadel Nielsen

The Lymantrid moth
Calliteara pudibunda L. is widespread in Danish beech (Fagus sylvatica)
forests. At rare occasions, populations suddenly and locally explodes and the caterpillers
occurs in huge numbers. The species has one generation in Denmark, with the dull grey moth
flying during June. Each female can lay 300-400 eggs which she normally does very near the
place where she emerged from the pupae. The small caterpillar is very hairy and can easily
be transported by the wind. In late autumn the caterpillar is fully grown, is about 5 cm
long and is very beautifully coloured. Pupation takes place among leaves on the ground
where a silken cocoon is made.

In the autumn 1998 a heavy attack of The Pale Tussock, Calliteara
pudibunda L. was observed in Dyrlev Wood, a beech wood 10 km north of Vordingborg on
the southern Zealand. The larvae defoliated particularly during August-September an area
of 20 hectares of the wood. As it can be seen from the illustrations, a very great amount
of the larvae had to starve and struggle themselves to death in their effort to get enough
food for the metamorphosis. Another big part of both larvae and pupae were destroyed by
parasites as fungi and parasitic wasps as the big and common Pimpla hypochondriaca.

In the spring, April, 1999, the author did not find very many cocoons
among the dead leaves on the forest floor, and in September 1999 it was estimated, (Jan
Martin), that the density of the attack had decreased with a factor 200 compared to the
previous year as is often the case with these mass attacks of C. pudibunda and
other Lymantriidae.

Fortunately no harm is done to the trees, as their growth is almost
finished when they are being defoliated by the caterpillars, and usuallly the moth
population returns to normal size within a season or two.

All photos by P. Stadel Nielsen

From the base of the tree to the top, caterpillars were walking up desperately trying to
find food, but only to fall down again and start all over. I was virtually raining with
caterpillars!

The colour of the caterpillar of D. pudibunda is normally yellow or bright green, but
when ocurring in such huge numbers, they get discoloured in mainly reddish, brownish or
greyish tones.

Many trees were surrounded by a 3 cm thick layer of caterpillars on the ground. Lots
of caterpillars were dead and the rotten smell of death was already noticeable!